A virtual machine (VM) technique, which causes a plurality of operating systems (OS) to run on a single server (a computer such as a workstation, a personal computer, and a server-only machine) so that one computer may be virtually used as a plurality of servers, has been known. As products using this type of technique, “VMWare (Registered Trademark) ESX Server” from VMWare Inc, “Virtual Server” from Microsoft (Registered Trademark) Corporation, and “Xen” from XenSource Inc. (US) have been known. By issuing a command to create a virtual machine, these products can create new virtual machines on a server.
In addition, a technique of transferring a virtual machine created on a server to another server in a distributed processor environment where a plurality of servers are connected through a network has been known. The technique of transferring a virtual machine has been described in Japanese Patent Application Laid-Open Patent Publication No. Hei 10-283210 (Patent Document 1), for example. Such a technique provides a function for transferring a virtual machine referred to as vMotion for VMware (Registered Trademark), and as migration for Xen.
In such an environment where a plurality of servers are distributed, since each virtual machine has a different performance requirement, which virtual machine is located on which server (hereinafter referred to as location of virtual machine) affects the effective performance of the virtual machine.
As a method of determining the location of a virtual machine, a method has been known in which, based on measurement data indicating the performance of existing virtual machines, the sum of the performance values is calculated for each of the possible combinations of respective virtual machines and respective servers, and each virtual machine is relocated in order to maximize the sum, which has been described in Japanese Patent Application Laid-Open Patent Publication No. 2005-115653 (Patent Document 2).    Patent Document 1 Japanese Patent Application Laid-Open Patent Publication No. Hei 10-283210    Patent Document 2 Japanese Patent Application Laid-Open Patent Publication No. 2005-115653
As described above, the techniques described in the patent documents determine the location of a virtual machine based on past performance data concerning a virtual machine to be located.
A first problem of the method is that the quick relocation of a virtual machine in response to a change in load on the virtual machine cannot be achieved.
The reason is that a sudden increase in load cannot be detected because the performance data has to be collected over a fixed period of time (typically, several minutes to several hours).
A second problem is that a situation occurs in which a system constructed on a virtual machine cannot be temporarily used.
The reason is that the system is temporarily stopped in the course of relocation because all the existing virtual machines become targets of the relocation.